Dockerfile: revert to Readline for debian frontend

Newt isn't available.

Signed-off-by: Paul Campbell <pcampbell@kemitix.net>
README.md: Remove comment about not including access method.

The base image includes a ssh server.

Signed-off-by: Paul Campbell <pcampbell@kemitix.net>
Dockerfile: perform actions in less transactions

Signed-off-by: Paul Campbell <pcampbell@kemitix.net>
Dockerfiler: break up the sdk update

Trying to make it more stable.

Disabled the upgrade of the SDK Tools as they aren't upgrading properly.

Signed-off-by: Paul Campbell <pcampbell@kemitix.net>
README.md: Update contents

Signed-off-by: Paul Campbell <pcampbell@kemitix.net>